Typical MEMS packaging systems mount a MEMS device to a die pad and the die pad is then hermetically sealed to a metal housing. In applications where the sensor is exposed to harsh environments, such as refrigeration and AC systems, a backside entry sensor is used because the top side of the sensor, which usually contains the piezo-resistive elements and connections to the package, cannot be exposed to the harsh conditions in the environment. The MEMS device is typically mounted on a die pad that provides a flange for mounting to the metal housing. The die pad includes a channel or port to the back side of the MEMS device. The flange of the die pad is then hermetically sealed to the metal housing. The metal housing surrounds the die pad and hermetically seals the channel or port of the die pad with a channel or port of the metal housing. The channel or port of the metal housing typically leads to an interface, such as a threaded interface, that allows the MEMS device to be coupled to a larger system. To this end, the die pad and metal housing combine to provide a hermetically sealed channel or port from the larger system to the back side of the MEMS device.
Typical MEMS systems including a die pad and metal housing have a number of deficiencies. For example, a number of different hermetically sealed interfaces must be executed and executed without defects. The MEMS device must be hermetically sealed to the die pad and the die pad must then be hermetically sealed to the metal housing. Each one of these seals must be maintained leak free for the life of the system.
In addition, because the MEMS device, die pad, and housing are usually made of different materials, the seals may be subject to thermal mismatch, which can cause cyclical stresses under thermal loading. Over time, the cyclical stresses due to thermal loading can affect the integrity of the seals. For all these reasons, the manufacture of MEMS systems with the typical construction discussed above may be complicated and include complex processes. These complex processes can lead to increased costs.
It would be beneficial if MEMS packaging designs could be simplified and some of the issues addressed above could be eliminated or ameliorated.